Lung cancer is a major international health problem. In the United States alone, an estimated 157,000 people will die of this disease in 2001 and tobacco use accounts for 85% of all lung cancers. Despite recent advances in cytotoxic drug development, radiotherapy and surgical management, the cure rate for advanced lung cancer remains poor. Further, much remains unknown about the molecular and genetic events involved in initiation and progression of lung cancer. One important mechanism seen in the development of epithelial cancers (i.e., lung cancer) appears to be underlying chromosomal instability due to a loss in telomere function brought about by significant cell division in the face of insufficient telomerase activity. Our laboratory has proposed that a combination of age-dependent epithelial renewal, somatic mutations that drive clonal proliferation, and chronic injury can accelerate telomere erosion, this culminating in a chromosomal fusion-bridge-breakage-translocation process. This process provides a mechanism for rapid and wholesale changes in cells, with rare cells incurring a threshold number of relevant changes to initiate the transformation process. Reactivation of telomerase or upregulation of alternative telomere maintenance mechanisms restabilizes the genome, allowing such initiated cells to expand and acquire changes resulting in a fully cancerous cell. I propose to build on the unique experimental attributes of the telomerase deficient mouse to develop a lung cancer model that is driven by mechanisms underlying the genesis of human lung cancer. A physiologic mouse model of lung cancer may be developed by exposing the telomerase deficient mice with shortened telomeres to chronic tobacco smoke: this will accelerate lung epithelial cell turnover and promote genome wide mutagenesis. Once validated, this model will be used to examine the role of telomerase activation during carcinogenesis, and as a tool for novel lung cancer gene discovery. The applicant is an M.D. who will have completed a residency in internal medicine with subspecialty training in adult medical oncology prior to the proposed start date. He also holds a Ph.D. in molecular biology and biophysics. The proposed research will be carried out in the laboratory of Dr. Ronald DePinho at the Dana Farber Cancer Institute.